The present invention relates to cellulose ethers having at least one phosphorus-containing substituent and to the mixed ethers thereof, and to a process for their manufacture in an aqueous alkaline medium which optionally contains an organic solvent.
Cellulose ethers which carry an anion-active substituent are used in many processes and fields of application, as water-soluble thickening agents and/or as auxiliaries, e.g., as a protective colloid, flocculating agent, binder and adhesive, dispersing agent or film-forming agent. Among these fields of application are the making of paper, the production and application of building materials, the processing of fibers, the preparation of pharmaceuticals and cosmetics, and the production of soaps and detergents, varnishes and paints, and food and luxury food. The best known commercial product of this type of cellulose ether is carboxymethyl cellulose (CMC) which is conventionally marketed in the form of its Na salt (NaCMC). Also gaining a certain importance are other carboxyalkyl ethers or sulfonoalkyl ethers of cellulose and mixed ethers which contain further ether groups in addition to the anion-active substituent, normally carboxymethyl. These include, for example, methyl carboxymethyl cellulose (MCMC), hydroxyethyl carboxymethyl cellulose (HECMC) or ethyl hydroxyethyl carboxymethyl cellulose (EHECMC).
Organic phosphonic acids or their derivatives lend themselves particularly well to the purpose of linking polybasic anion-active substituents to the cellulose ether molecule. The reaction of cellulose with reactive, organic phosphonic acids or derivatives thereof (e.g., halogenoalkane phosphonic acids) results in cellulose ethers which have a phosphonic acid group or one of its salt forms in their ether substituent. These cellulose ethers which contain phosphonic acid groups are often insoluble in water, because reaction, for example, with halogenoalkane phosphonic acids to give more than a very low degree of substitution is difficult. However, water-soluble products have also been disclosed.
U.S. Pat. No. 2,979,374 and the paper "Phosphonomethylation of Cotton" by G. L. Drake, W. A. Reeves and J. D. Guthrie, published in Textile Research Journal, March 1959, pages 270 to 275, describe chemically modified, fibrous textile materials based on cellulose and a process for preparing these materials, in which certain of the hydroxyl groups of the polysaccharide are replaced by --O--CH.sub.2 --PO.sub.3 X.sub.2 groups, wherein X is either H or an alkali metal or NH.sub.4. The degree of modification ranges from 0.01 to 4 percent by weight of phosphorus. In the process for the preparation of these products, the fibrous starting material is reacted with an aqueous solution of an alkali metal salt of chloromethane phosphonic acid or another salt of this acid and an excess of alkali metal hydroxide. The products obtained may be further converted to the free acid form or to the corresponding ammonium salts. It is also possible to prepare water-soluble phosphonomethyl ethers of cellulose, if the degree of modification is chosen in such a way that at least 2 percent by weight of phosphorus is introduced. The starting materials mentioned include cotton fibers, cellulose hydrate fibers, aminized cotton fibers, carboxymethylated cotton fibers, paper and sulfonoethylated cotton fibers. For the purpose of introducing the phosphonomethyl groups, either a metal salt of chloromethane phosphonic acid itself or its acid chloride may be used; it is also possible to use the corresponding monoesters or diesters.
The crosslinked phosphonoalkyl celluloses according to German Offenlegungsschrift No. 26 00 930 (corresponding to U.S. Pat. No. 4,020,271) comprise basic molecules of a kind which, without crosslinking, would themselves be water-soluble, but which are rendered substantially water-insoluble by crosslinking with formaldehyde, epichlorohydrin, dichloroacetic acid, diepoxides or other known difunctional components. With respect to carrying out the etherification stage, reference is made to the previously mentioned U.S. Pat. No. 2,979,374.
The methods for the preparation of ion exchangers according to German Auslegeschrift No. 20 05 407 (corresponding to U.S. Pat. No. 3,634,394) or according to German Auslegeschrift No. 20 05 408 (corresponding to U.S. Pat. No. 3,652,540) can also result in products which carry a phosphonomethyl group. In one method, for example, pearls of regenerated cellulose are reacted in toluene in the presence of benzethonium chloride [CH.sub.3 -C(CH.sub.3).sub.2 -CH.sub.2 -C(CH.sub.3).sub.2 -C.sub.6 H.sub.4 -(O-CH.sub.2 -CH.sub.2).sub.2 -N.sup..sym. (CH.sub.3).sub.2 -CH.sub.2 -C.sub.6 H.sub.5,Cl.sup..crclbar. ] with a solution containing NaOH, NaBH.sub.4, water and chloromethane phosphonic acid for 16 hours at a temperature of 90.degree. C. The product obtained is insoluble in water.
The basic cellulose structures of the phosphonopropyl celluloses according to Soviet Union Inventor's Certificate No. 596,593 possess ether substituents of the general formula ##STR2## wherein R represents a hydrogen atom or a lower alkoxy group, and R' represents an alkali metal or a lower alkyl group. Thus, these products are neither phosphonic acids or their mono- or disalts, nor are they alkylphosphinic acids or their salts, such as are claimed in this invention. For preparing these compounds, the following procedure is used: allyl cellulose is reacted with alkali metal salts of hypophosphorous acid or with dialkyl phosphites (dialkyl esters of phosphorous acid) in the presence of organic peroxides, at temperatures between 80.degree. and 100.degree. C.
There have also been proposed processes for the preparation of cellulose ethers or cellulose mixed ethers which, as substituents, exclusively contain phosphonomethyl groups with substituents where, on the one hand, the method of processing has been improved as compared with the state of the art described above, while, on the other hand, novel reaction products result in some cases.
The not prepublished German Offenlegungsschrift No. 30 39 978 discloses a process for preparing water-soluble phosphonomethyl ethers of cellulose, which are made from cellulose and halogen methane phosphonic acid or one of its salts or acid derivatives. The reaction medium contains from 2.1 to 15 moles of hydroxide ions and from 0.4 to 3.0 moles of halogenomethane phosphonate ions as the etherifying agent and, in addition, from 3 to 50 parts by weight, per part by weight of cellulose, of a mixture which is composed of water and an organic solvent, such as isopropanol. The degree of substitution (DS.sub.PM) of the reaction product shall be at least 0.13.
Also, in German Offenlegungsschrift 30 39 963, which has not been prepublished, water-soluble mixed ethers of cellulose are described which contain (a) at least one substituent from the group comprising alkyl, hydroxyalkyl, carboxyalkyl, sulfoalkyl and dialkylaminoalkyl, and (b) a phosphonomethyl substituent. The degree of substitution (DS or, respectively, MS) of the substituents under (a) thereby is from 0.05 to 2.95 for the DS, respectively from 0.5 to 6.0 for the MS.sub.HAlk, and from 0.005 to 0.8 for the DS.sub.PM. A process for the preparation of these mixed ethers is carried out in a way similar to that for the preparation of the pure ethers described above.